1. Field of the Invention
The present invention relates to an optical fiber illumination device which irradiates illumination light onto a medium to be inspected, such as a card, and an inspection apparatus which inspects a medium to be inspected, such as a hologram-attached paper instrument.
2. Description of the Related Art
A diffraction optical variable device (to be referred to as optical OVD), a typical example of which is a hologram, is a device processed to induce the light diffraction phenomenon on the surface thereof, and it has a pattern which generates vivid colors due to optical diffraction and interference caused by the diffraction pattern. The hologram has optical characteristics different from those of the ordinary printing and therefore it is used as a security thread for paper instruments of, for example, coupons and securities as well as cards such as credit cards. Thus, the hologram is realized as means for determining the authenticity of these media.
On the other hand, for the purpose of quality control of hologram-attached paper instruments and cards, various inspection apparatuses are used to inspect holograms attached to the paper instruments and cards. For example, Jpn. Pat. Appln. KOKAI Publications No. 2004-150885, No. 2002-221494 and No. 2002-221496 disclose an inspection apparatus which irradiates a laser beam on a surface of a medium to be inspected and inspects the reflection diffraction image with a light receiving sensor, an apparatus which inspects a moving medium to be inspected with a line illumination, etc.
As the inspection apparatus, a type which identifies the authenticity of a hologram is conventionally known. In this apparatus, light is applied onto the hologram at a predetermined angle and the light receiving system is placed at a position where the diffraction light is emitted. For example, Jpn. Pat. Appln. KOKAI Publication No. 2001-307173 discloses an inspection apparatus which identifies the authenticity of a hologram, using a spotlight system which projects measurement light, and a plurality of light-receiving systems respectively detecting a plurality of reflection diffraction light components reflection-diffracted by the diffraction pattern of the hologram. Further, Jpn. Pat. Appln. KOKAI Publications No. 2002-221494 discloses an illumination device which illuminates a hologram, in which a plurality of Selfoc (trademark) lenses are arranged at predetermined angles to irradiate light onto the hologram.
In general, an illumination device which uses optical fibers that is less expensive as compared to Selfoc lenses, includes an optical fiber light guide, in which the elemental fibers of the optical fibers are arranged to be vertical to the light-emitting surface of the optical fiber light guide. One end of the optical fiber light guide is located on the light source side, and the light emitted from the light source is transmitted through the optical fiber and emitted from the other end of the optical fiber light guide.
However, the conventional inspection apparatus of the type which utilizes laser light entails such drawbacks as that the conditions for stopping the medium to be inspected for observation are severe, and it requires much time to collect information and for identification process. The conventional inspection apparatus designed to inspect a moving medium entails such a drawback that the rattling of the medium to be inspected causes an adverse effect to the results of the inspection.
Further, paper instruments such as of securities, as they are circulated, will wear down so that the surface condition thereof deteriorates due to chipping, peeling-off, cut, wrinkle, etc., and accordingly there is a possible that the basic optical characteristics of the hologram are lost, which is called “fatigue”. For the apparatus which automatically inspects these paper instruments, it is required to inspect the authenticity (genuine or counterfeit) as well as the damaged state. However, there has been no such apparatus provided to inspect such damage, fatigue, etc. of the hologram.
In order to detect reflection diffraction light from a hologram, it is necessary to apply light onto the hologram at a specific angle. In the case where the light is irradiated onto the hologram at a specific angle using a conventional optical fiber light guide, the light-emitting surface of the optical fiber light guide is set to be inclined at a specific angle with respect to the hologram. In the region where the light is applied, the light is strong and concentrated in a section close to the light-emitting surface of the optical fiber light guide, whereas the light is weak and diffused in a section far from the light-emitting surface. As a result, the spreading of the light and the light intensity within the view field to be detected is uneven. A hologram inspection apparatus that uses such an illumination is not able to stably obtain the data within the entire view field to be inspected, which causes an adverse effect on the inspection accuracy.